"That which is lawful is plain and that which is unlawful is plain and between the two of them are doubtful matters about which not many people know. Thus he who avoids doubtful matters clears himself in regard to his religion and his honor, but he who falls into doubtful matters falls into that which is unlawful, like the shepherd who pastures around a sanctuary, all but grazing therein. Truly every king has a sanctuary, and truly Allah's sanctuary is His prohibitions. Truly in the body there is a morsel of flesh which, if it be whole, all the body is whole and which, if it be diseased, all of it is diseased. Truly it is the heart." [Bukhari and Muslim]

The clear halal is that which has no element of haram, such as rain water which is falling on one's own property.

The clear haram is that which has some haram element, be it in substance (such as pork, or eating in gold vessels) or in manner of acquisition (such as riba, or a bribe).

The doubtful is that which is between these, and we can discuss it under the following three sections :

A. WHERE THERE IS DOUBT WHETHER THERE HAS OCCURRED A PROCEDURE WHICH RENDERS THE PERMISSIBLE IMPERMISSIBLE, OR VICE-VERSA

There are four cases:

1) That the original prohibition is known, and then doubt ensues as to whether the procedure for rendering permissible has occurred.

e.g. A hunter wounds an animal, which he later finds dead in the water, such that he is unsure whether it died from the wound or from drowning.
It is obligatory to keep away from this category of uncertainty.

2) That the original permissiblity is known, and then doubt ensues as to whether some process rendering it haram has occurred.

e.g. One man says that if the next bird to fly past is a crow, then his wife is divorced, and another man says that if it is a raven then his wife
is divorced. Then, a bird flies past, but its identity cannot be determined. In this case, neither of the wives are divorced.

It is precautonary to abstain from things in this category of uncertainty.

3) That the default prohibition is known, but reasonable conjecture suggests that the process of rendering halal has occurred.

e.g. A hunter wounds an animal, and then later catches up to it, to find it dead, with no mark on it other than the wound he inflicted.
The apparent status of this category is that of permissibility.

4) That the original permissibility is known, but reasonable conjecture suggests that a process of rendering haram has occurred.

e.g. there are two containers of water; if one arrives at the conclusion that the water of one of the containers is unclean, based on certain indications that one sees in it, then it is not permissible to use that water for drinking, nor for wudu'.

B. DISPERSION OF HALAL AMONGST HARAM

There are three cases:

1) Where a finite quantity of haram has become mixed with a finite quantity of halal.

e.g. a single dead animal (or a finite number of dead animals) becomes mixed amongst a finite number of correctly-slaughtered animals.

It is obligatory to abstain from them all.

2) Where a finite quantity of haram has become mixed with a non-finite (i.e. extremely large) quantity of halal.

e.g. someone who was separated from his sister at birth, such that he does not know her, although they continue to live in the same large city.
In this case, he is not required to abstain from marrying a woman from the same city, for that would pose a hardship.

A claim of precaution in such a case is a false misgiving.

3) Where a non-finite (i.e. very large) quantity of haram has become mixed with a non-finite (very large) quantity of halal.

e.g. as is the case nowadays, when money from riba, bribery, etc is in wide circulation in the market.

In this case, it is not prohibited to partake of something of the entire quantity, unless there is some indication that this particular amount or
portion is from the haram. Otherwise, to abstain from it is precautionary, but not forbidden.

C. ASKING

The only valid motivation for asking someone about the source of what s/he is presenting to you is the existence of some suspicion about it. This may
occur in one of two ways:

1) There is something suspicious about the person

e.g. his appearance is unquestionably that of a criminal, or he is wearing the uniform of an oppressive army.

In the absence of any such indication, it is neither obligatory nor even permissible to ask him, because it would involve distressing a Muslim without basis. Nevertheless, to abstain (without asking) is precautionary.

2) There is something suspicious about that which you are being given

e.g. if it is known that some stolen goods have found themselves into the market.

In this case, it is not obligatory for buyers to ask about the source of the merchandise, unless it transpires that the majority (of that available
in the market) is haram. Otherwise, abstention is precautionary. Similar is the case of accepting a gift from someone who has both halal and haram
sources of income. However, if the person is unreliable, or has some vested interest in your accepting that which he is giving you (gift or
merchandise) then his word is of no value, and one should ask someone else.